1. Field of the Invention
This invention relates to a novel phosphoric ester and, more specifically, to a phosphoric ester having serine or its salt as a substituent.
2. Description of the Prior Art
Heretofore, as those phosphoric esters having nitrogen-containing polar groups such as amino or ammonium groups in the molecule, phospholipids typically represented by natural phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl serine and sphingolipid have been well-known. Since these phospholipids contain both hydrophobic and hydrophilic groups in one molecule and show interfacial activity such as surface activity and emulsification activity, they are used in various fields.
Further, it has been known that these phospholipids exist in a large amount in the cells of living bodies and are a main component of bio-membranes. It has been gradually made clear in recent years that these lipids not only exist as the constituents for the bio-membranes in the living body but provide various important physiological effects in the living body. For instance, it has been elucidated that the platelet activating factor (PAF) which is one of ether type phospholipids having a structure similar to that of phosphatidyl choline exhibits antihypertensive, hemolizing and immunologically active effects in an extremely small amount. It has also gradually been made clear that the phosphatidyl serine contributes to various life activities by activating, under the coexistence of diglyceride and calcium ions in the living body, the protein kinase C which is a phosphorylating enzyme independent of adenosine triphosphate (ATP). Furthermore, it has also been disclosed that lysophosphatidyl serine obtained by hydrolyzing the acyl group on the 2-position of phosphatidyl serine is involved with allergy reactions or the like.
Accordingly, it has also been expected that those materials similar in structure to the phospholipids having the above described bioactivities, that is, those phosphoric esters having nitrogen-containing polar groups such as amino or ammonium groups in one molecule have various activities and functions. Development of phosphoric esters has been desired which are homologues of phospholipids having nitrogen-containing polar groups such as amino groups and are capable of being synthesized in high purity in a simple procedure using inexpensive and easily available starting materials.
However, since the synthesis of phospholipids is generally very difficult and requires in most cases multi-stages of reactions, the aimed compounds can be obtained only in low yield (for instance refer to E. Baer, et al in Journal of the American Chemical Society, 72, 942 (1950) and "Lipids" edited by Tamio Yamakawa, published from Kyoritsu Shuppan (1973)).
Further, some studies have been reported for the synthesis of phosphoric esters having the structure similar to the phospholipids. However, they require multistages of reactions and starting materials difficult to be synthesized, separation of the aimed product after the reaction is often difficult, the yield is low and the performances of the thus obtained compounds are often insufficient (for example, refer to Japanese patent publication Nos. 23330/1967 and 1654/1973, U.S. Pat. No. 3,507,937).